Answers
1

They were horrified because before this no animal had ever killed another animal.

They were shaken and miserable. They did not know which was more shocking - the treachery of the animals who had leagued themselves with Snowball, or the cruel retribution they had just witnessed. In the old days there had often been scenes of bloodshed equally terrible, but it seemed to all of them that it was far worse now that it was happening among themselves. Since Jones had left the farm, until today, no animal had killed another animal. Not even a rat had been killed. They had made their way on to the little knoll where the half-finished windmill stood, and with one accord they all lay down as though huddling together for warmth - Clover, Muriel, Benjamin, the cows, the sheep, and a whole flock of geese and hens - everyone, indeed, except the cat, who had suddenly disappeared just before Napoleon ordered the animals to assemble.